Implementation and documentation updated - now allows for pure-esm to…

… be imported into cjs

README.md

@@ -50,6 +50,8 @@ Synchronously import dynamic ECMAScript Modules similar to CommonJS [require](ht
 
 Basic wrapper around [esm](https://github.com/standard-things/esm) for compatibility with both ES6 and CJS projects in NodeJS
 
+Capable of importing pure-esm libraries such as node-fetch@3 in CJS projects
+
 [![Try with Replit](https://replit.com/badge?caption=Try%20with%20Replit)](https://replit.com/@nktnet1/import-sync-example#index.js)
 
 </div>

src/import.ts

@@ -1,21 +1,36 @@
+import esm from 'esm';
 import path from 'path';
-import { getCallerFilePath } from './files';
+import fs from 'fs';
 import { ESMOptions, Options } from './types';
 
 /**
  * Creates an esm-compatible require function that can import ES Modules
  *
- * Removes the error for "[ERR_REQUIRE_ESM]: require() of ES Module", as per
- * - https://github.com/standard-things/esm/issues/855#issuecomment-657982788
- *
  * @returns an ESM-compatible require function
  */
+/* istanbul ignore next */
 const createEs6Require = (esmOptions: ESMOptions) => {
-  /* istanbul ignore next */
+  /**
+   * Removes the error for "[ERR_REQUIRE_ESM]: require() of ES Module", as per
+   * - https://github.com/standard-things/esm/issues/855#issuecomment-657982788
+   */
   require('module').Module._extensions['.js'] = (m: any, filename: string) => {
-    m._compile(require('fs').readFileSync(filename, 'utf-8'), filename);
+    m._compile(fs.readFileSync(filename, 'utf-8'), filename);
+  };
+  const loader = esm(module, esmOptions);
+
+  const newModule = module.constructor.length > 1 ? module.constructor : loader('module');
+  const oldResolveFilename = newModule._resolveFilename;
+  /**
+   * Referencing
+   * - https://github.com/kenotron/esm-jest/commit/624b9524ee698f5cbd16ee2481dc4cd0dec52e42
+   * - https://github.com/standard-things/esm/issues/331#issuecomment-377056717
+   */
+  newModule._resolveFilename = function(request: string, parent: any, isMain: boolean) {
+    const newRequest = request.startsWith('node:') ? request.substring(5) : request;
+    return oldResolveFilename.call(this, newRequest, parent, isMain);
   };
-  return require('esm')(module, esmOptions);
+  return loader;
 };
 
 /**
@@ -26,13 +41,13 @@ const createEs6Require = (esmOptions: ESMOptions) => {
  * @param {Options} [options] - options as defined in types.ts
  * @returns the imported module
  */
-const importSync = (relativePath: string, options: Options = {}) => {
+const importSync = (id: string, options: Options = {}) => {
   const defaultOptions: Required<Options> = {
-    basePath: path.dirname(getCallerFilePath()),
+    basePath: require.main?.path || '',
     esmOptions: {},
   };
   const opts = { ...defaultOptions, ...options };
-  const filePath = path.join(opts.basePath, relativePath);
+  const filePath = path.join(opts.basePath, id);
   const es6Require = createEs6Require(opts.esmOptions);
   try {
     return es6Require(filePath);